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Hi all, can anyone point me in the right direction in getting a harmonic damper for my supercharged TR4 project. It has to be serpentine belt driven which basically means I have to have one fabricated, I have contacted ATI in the states about their superdampers but they not taking on fabrication work on in the near future, I could modify a standard TR4 superdamper if anyone has one out there? Other than that anyone know of a fab shop that could make me one?

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Hi Deano,

I don't know much about the science of crank dampers but there must be some basics that should be considered.

 

What are you trying to damp?

The rattler above is for torsional problems - the TR4 crank does not suffer in this area. Failures are due to flexing and usually at the #4 big-end to web radius.

 

Is it to damp harmonic vibration? what frequency?.

Dampers tend to operate in a limited range. You need to know what this is.

 

The TR4 never had a harmonic damper - is ot really required.

 

People put MGB dampers on TR's - why!!!

 

Roger

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Hi Roger, thanks for the reply, have had this discussion many times already, Revington suggests no damper, but racetorations and Tr enterprises both do, I also realize that that due to supercharging the engine that I will never need to rev beyond 5000 to get good power. Maybe it's just me being anal but having spent a fair few quid on the engine it justs put my mind at ease even if I don't need it.

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If I remember my 4 pot folk law, the engine goes through an harmonic period at 5200 and again at 5800, so race engines and (V) fast road engines 'may benefit' from a damper

 

I expect to be corrected as I get my coat and leave the building..... :ph34r:

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Hi Roger, thanks for the reply, have had this discussion many times already, Revington suggests no damper, but racetorations and Tr enterprises both do, I also realize that that due to supercharging the engine that I will never need to rev beyond 5000 to get good power. Maybe it's just me being anal but having spent a fair few quid on the engine it justs put my mind at ease even if I don't need it.

You do need a damper .

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Hi Deano,

I don't know much about the science of crank dampers but there must be some basics that should be considered.

 

What are you trying to damp?

The rattler above is for torsional problems - the TR4 crank does not suffer in this area. Failures are due to flexing and usually at the #4 big-end to web radius.

 

Is it to damp harmonic vibration? what frequency?.

Dampers tend to operate in a limited range. You need to know what this is.

 

The TR4 never had a harmonic damper - is ot really required.

 

People put MGB dampers on TR's - why!!!

 

Roger

'4 Cylinder TR Folk Lore' as we knew it, said the great propellor on the front of the crank was a type of harmonic balancer, due to its rubber mounting, and removing it would cause catastrophes - Then again I have seen road going TR's with broken cranks that had and did not have the standard fan arrangement.

 

I for one ditched the standard cooling fan in 1972 on my first TR in favour of a windscreen wiper motor, Escort plastic fan and bit of Mecano. That system worked a treat until 1979 when I got a good used Kenlowe, whose real benefit was that it moved more air.

 

I am not aware of any science behind why the MGB pulley/damper is used. I think the MGB crank damper gets used for narrow belt conversion as it is a cheaply available pulley with the right sized bore & keyway to fit a TR crank. The only fiddle is the seal area diameter which is dealt with by the use of a sleeve . The specialists have had it remade for the billions of failing MGB's out there and the TR fraternity enjoys a spin off to give a narrow belt conversion.

Peter W

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I am not aware of any science behind why the MGB pulley/damper is used. I think the MGB crank damper gets used for narrow belt conversion as it is a cheaply available pulley

 

Hi Pete,

availability and cheap is not engineering. Where is the science behind fitting a damper not designed for the job.

 

I have a theory why the 4 pot cranks break and it has nothing to do with the fan. (based on engineering, levers and forces)

 

Roger

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Hi Pete,

availability and cheap is not engineering. Where is the science behind fitting a damper not designed for the job.

 

I have a theory why the 4 pot cranks break and it has nothing to do with the fan. (based on engineering, levers and forces)

 

Roger

Can you pm me with your thoughts on this Roger?

Peter W

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Can you pm me with your thoughts on this Roger?

Peter W

Can I ask for your thoughts via PM also please Roger.

 

Mick Richards

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Roger,

I'm sure many would like to share your expertise - I know I would, please.

Save yourself multiple mailings and post them here? No one could complain of a thread hijack!

John

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Hi Folks,

these are my thoughts.

There is no mathematical backing except for a good grounding in engineering.

 

breaking of the crank.

Most breakages occur at the #4 big-end journal to web radius.

I know of only one break elsewhere and that was near #2 big-end.

It doesn't break because the number 4 is unlucky etc there must be a reason.

We know that the crank flexes, and I believe this is the cause but not the main problem. How does it break.

#1 Main bearing (front) - the #1 piston/con rod moving up/down causes the crank to flex. On the other side of the MB is the fan or possibly no fan. So the crank flexes up and down with nothing to stop it. There is a tilting of the crank in the MB thus removing some of the flexing forces.

#2 MB (middle) - the #2 & 3 pistons go up/down together. at the top or bottom of the stroke the crank bends but not equally

When one is on the power stroke the other is on the induction. So there is less of a bend - more like a tilting in the MB

This minuscule tilting removes much of the bending forces. in the next cycle it flexes the other way.

#3 MB (rear) - #4 piston goes up/down. Flexing will try to take place BUT the flywheel, spinning at whatever revs, is effectively a solid structure. No tilting can take place thus ALL the flexing forces are centred about an area near the rear of the crank.

One would think that the web to MB journal would take the brunt but it is quite big and being on the centreline does not have the greatest flexing.

The #4 big-end journal to web radius, which is immediately forward of the MB, takes all/most the flexing (the web is effectively stuck to the MB journal and thus solid).

Eventually the #4 big-end lets go. It is a tensile failure not a torsional failure.

if the radius is not machined well or any imperfections exist in the radiu then failure will happen sooner rather than later.

It is all about flexing of the crank and tilting in the MB (or not, in the case of the rear main bearing).

Flexing happens and the crank is designed to do this. The material is EN16 and that is happy with flexing.

Tilting happens and is a good thing

It is the stiffness that the flywheel imparts on the structure that causes the cracking and this is fed along the chain to the weakest area #4 journal/Web radius.

I hope that makes sense.

Roger

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As the flywheels got heavier from TR2 onwards are there more breakages on later engines compared to earlier or doesnt that make any difference.

Stuart.

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Hi Stuart,

that is a very good question. I would think the absolute answer would be yes because the heavier flywheel would be that much stiffer structure

(greater precession forces).

However there must be a point where it is heavy enough to transfer any excess loads to the #4 BE (the weakest point).

 

Perhaps a lighter flywheel may move problems somewhere else (or perhaps nowhere).

 

I have no stats on crank breakage distribution. It would have been a good project recording the breakages over the decades as they happened.

 

Roger

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Aside from the internals isn't the crank damper also to try and remove the pulsing from the belts on the ancillaries such as Alternator? I am aware that alternators now often / always have their own inbuilt damper.

 

Alan

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I can imagine the fact that #4 also transmits the torque generated by the previous pistons also plays a role.

The resultant stresses in each journal are a combination of bending, sheer and torsional stresses (although sheer is probably small in this case).

Surface imperfections luke sharp edges as indicated by Roger can act as stress risers, and lead to failure, even if general stress levels may be acceptable.

It is beyond my capabilities to do any calculations, dynamic loads are very complex.

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Hi Waldi,

you make a good point.

 

#4 BE journal should only be loaded with shear loads.

However because there is flexing (albeit extremely minuscule) this changes various angles very slightly and you get a vector of tensile load.

 

The Main Bearing journal to web suffers the torsional loading - but has survived well.

 

The answer would be a five bearing crank, but it is a bit late now.

 

Roger

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The problem for the crank is not the normal force applied

on any working state. That is what it is made for.

 

The problems rise at resonant frequencies where we know

a lot of examples where bridges collapse or glass breakes.

 

For our cars this means that driving straight through these

frequencies is not good but not that problem.

A real stress is to have a constant rpm at that resonant state,

lets say to drive the TR4 at those 5400 rpm or so.

 

The crank is twisted and a new bending pulse is added at the worst moment

to increase the amplitude even more.

That is much, much more than a simple pulse from a firing cylinder can cause.

 

Normally a TR6 can run in that state but a TR4 not.

Also the longer the crank the more this is a problem

that must be taken into account. Thats why a TR6 has a damper.

 

So the remedy is easy: The damper does no harm but can help a lot.

If the TR4 will se often more than 5000rpm I would fit one.

 

These rubber/Steel dampers are made to damp a special frequency

they must be made for a special engine to meet the requirements.

The sillicone oil/steel ring dampers work in a long range and

are more universal but heavier.

 

Normally the damper is at the front and at the rear we have a lot of mass

from flywheel and clutch that we expect this area to have a very low

torsion frequency that plays not that role in our dangerous torsion frequencies.

 

I made my own pulley from the original damper where I put the rib belt pulley like a cup

over the original pulley in my V8 project because there was no space but I needed the

5 rib belt. Was a lot of work to cut all that material out of a massive 200mm steel piece

but as there was nothing suitable availiable it was the only solution.

I would not take aluminium because it wears quickly.

 

One word to stress to the crank and a blower: The crank is not made to accept a big load

at the front to drive a blower. So the toothed wheel must be mounted as narrow to the block

as possible otherwise the chance rises that the front of the crank pops off.

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